I’ve been asked a lot recently about whether or not sourdough can be eaten by those with a gluten allergy. There seems to be a rumor going around that sourdough is a good gluten-free alternative. Here are the facts:
Sourdough bread is not gluten free. It’s made with wheat flour, and as yet there is no way to completely remove gluten from wheat flour. Not even close. There is under development a process by which the gluten can be completely broken down in the flour during the fermentation part of bread making, but it takes a very long time under very tightly controlled circumstances. As far as I know, there are no commercially made breads using this process available on the market.
In short, if you suffer from a severe case of celiac disease, do not eat sourdough bread.
However, if you are gluten sensitive or gluten intolerant you might experiment with homemade sourdough to see if you can tolerate it. Here’s why it might work:
There’s been an uptick in interest in artisan and naturally fermented products, recently, and their relationship to gut health (which has been linked to everything from skin care to autism). To understand why sourdough sometimes gets a gluten pass, it helps to understand how sourdough gets made. (This will also help you to know when a bread is really sourdough and when it merely tastes sour.)
Sourdough bread is made with natural yeast. Yeast is pretty much everywhere in our environment. That dusty-looking film on the skin of grapes is a sign of yeast activity. It especially likes to collect on fruit — it’s easy to get from strawberries too. It’s blowing around in the air and attaching itself to all kinds of plants. The yeast that makes sourdough bread is the same stuff our ancestors used to make wine and beer, and has, beginning in the late 19th century, been isolated and selectively bred to create commercial yeasts for these purposes, to produce specific flavors and aromas resulting from the fermentation activity particular to those strains.
Yeast is a fungus, and in bread making it feeds on wheat flour starch — not gluten. Gluten is what makes the dough stretchy, so that it can trap the CO2 the yeast releases as it feeds and grows. C02 is what gives your sourdough bread those lovely holes for butter to sink into — and it’s what makes the bread rise. Gluten is very difficult for some people to digest — it’s a strong, tough series of molecules that are not easily broken down quickly. This is where natural yeasts come in.
Natural yeasts, compared to commercial yeast you buy at the store, are very weak. Commercial yeast has its wonderful uses but it’s like a mutant superhero compared to the wild yeasts blowing around your environment. The most common commercial yeast, Saccharomyces cerevisiae, and its subspecies, has been isolated and concentrated in the active dry yeast you find in supermarkets, so that it can get to work very quickly. It goes into a ball of dough and immediately eats up all the starches, creating lots of C02 and rising the dough in a matter of a couple hours. However, gluten takes much longer to break down, so its structure remains largely unchanged by the quick process of commercial yeast bread making.
Sourdough breads like the ones I make take about 48 hours start to finish. The starter, containing natural yeasts, gets mixed with the flour and gently pulled and stretched at regular intervals over 3–4 hours before it is shaped into loaves. This activates the gluten molecules, softens and begins to break them down, and helps them to form longer and longer strands, so that the air pockets in the dough will be able to inflate like a balloon, making the bread rise nicely in the oven. After the loaves are shaped, they go into the refrigerator for about 24 hours. This allows the gluten time to further relax and break down. The slowness of the natural yeasts, which are further slowed by being refrigerated, is what allows the gluten time to relax and break down.
The process by which the gluten is broken down has little to do with the actual yeast activity. Gluten is broken down by hydrolysis — the chemical breakdown of a compound by water. The importance of using wild-caught yeasts is that hydrolysis takes a long time to work, and so do the natural yeasts in our environment, when compared to commercial varieties. In fact, some bread makers “autolyse” their flour by mixing it with water and allowing it to rest for anywhere from 10 minutes to several hours before adding the sourdough starter, giving the hydrolysis process a head start over fermentation. The net result of all of this chemical and enzymatic activity is that by the time it gets eaten, the gluten is much easier to digest because it’s been partially broken down already!
The sourness of sourdough bread is a byproduct of bacterial activity. Lactobacilli, the bacteria which coexists with the wild-caught yeast, feeds on the starchy sugars that the yeast fungus cannot digest, producing lactic and acetic acid. That’s what gives the bread its sharp flavor. If you buy packaged, pre-sliced sourdough bread from the supermarket, check the ingredients on the back. If “citric acid” is listed, don’t expect that the long gluten-relaxing process was observed. They’ve likely just added the sour-tasting salt to the dough to mimic the qualities of sourdough bread without any of the digestive benefits.
In the end, your ability to tolerate sourdough bread will come down to the specific requirements of your own body, and that is a science project that requires careful and responsible testing methods. Be kind to yourself and do your homework!